Medical imaging can provide health professionals with information about the anatomy, physiology, and histology of humans and animals. Images can be displayed and acquired in both two and three dimensions. In some imaging procedures, a contrast agent is used to accentuate differences between a region of interest and surrounding tissues. Some contrast agents, for example, have an affinity for particular types of tissues or cells, e.g., cancerous cells. When introduced to a subject, the contrast agent tends to concentrate near cancerous cells allowing the visualization of otherwise hidden cancers. Other contrast agents may lack a particular affinity for a particular cell or tissue. Such contrast agents may be used to, e.g., visualize pathways such as vessels and lymph ducts.
One application of medical imaging is to perform sentinel lymph node (SNL) mapping. In this technique, a health professional seeks to identify lymph nodes associated with a cancerous tumor. The underlying hypothesis behind SNL mapping is that the first lymph node, defined as the SLN, to receive lymphatic drainage from a tumor site will exhibit tumors if there has been lymphatic spread. If no malignant cells are found in the SLN during frozen section analysis in the operating room, then the patient is spared the significant morbidity associated with a radical dissection of all lymph nodes surrounding the tumor. In breast cancer, for example, auxiliary node dissection, and its associated lymphedema, can be avoided in patients whom the SLN is negative histologically. Another benefit of SLN mapping is that it affords a regional control in patients with palpable tumor-containing nodes.
Sentinel lymph node mapping and resection are presently the standard of care for both breast cancer and melanoma. Although tumors that are already malignant at the time of resection may not benefit from SLN mapping, large clinical studies have shown that only approximately 5% of SLN-negative breast cancer patients will manifest metastatic disease at a later time. These results suggest that SLN mapping and resection may be a reasonable approach for most solid tumors, and indeed, clinical studies in colon cancer have already begun.